
class Solution {
    public ListNode mergeTwoLists(ListNode list1, ListNode list2) {
        if(list1 == null){
          return list2 ;
        }else if(list2 == null){
          return list1 ;
        }else if(list1.val < list2.val){
          list1.next = mergeTwoLists(list1.next , list2) ;
          return list1 ;
        }else{
          list2.next = mergeTwoLists (list1 , list2.next) ;
          return list2 ;
        }

    }
}